Combined motor drive and automated longitudinal position translator for ultrasonic imaging system

ABSTRACT

A vascular imaging system with an automated longitudinal position translator includes a drive unit with a single motor to provide for rotational and longitudinal translation of a drive-cable and distally mounted transducer within a catheter assembly. The drive unit includes a main body casing and a pullback carriage on which the main body casing slidingly engages. The drive-cable is mechanically coupled to the motor, and an outer sheath of the catheter assembly is fixed to the pullback carriage via a rigid pullback arm. The imaging system can be made to operate in an automated longitudinal translation mode, wherein the main body casing of the drive unit is made to uniformly and longitudinally move relative to the pullback carriage by the drive unit motor, thus causing coincident longitudinal movement of the drive-cable (and distally located transducer) relative to the outer guide sheath of the catheter assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 09/074,064, filedMay 7, 1998 now U.S. Pat. No. 6,004,271. The disclosure of the priorapplication is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention pertains generally to diagnostic and therapeuticultrasonic imaging systems and, more particularly, to apparatus forproviding automated longitudinal position translation in ultrasonicimaging systems.

BACKGROUND OF THE INVENTION

Probe assemblies having therapeutic and/or diagnostic capabilities arebeing increasingly utilized by the medical community as an aid totreatment and/or diagnosis of intravascular and other organ ailments. Inthis regard, U.S. Pat. No. 5,115,814 discloses an intravascularultrasonic imaging assembly with a distally located imaging element thatis positionable relative to intravascular sites. Operation of theimaging element in conjunction with associated electronic image recoverycomponents generates visible images that aid an attending physician inhis or her treatment of a patient's vascular ailments. In particular, aphysician may view in real (or essentially near real) time intravascularimages generated by the ultrasonic imaging probe element to locate andidentify intravascular abnormalities that may be present and therebyprescribe the appropriate treatment and/or therapy.

The need to accurately position a distally located operative imagingelement relative to an intravascular site using any therapeutic and/ordiagnostic probe assembly is important so that the attending physiciancan confidently determine the location of any abnormalities within thepatient's intravascular system. Accurate intravascular positioninformation for the imaging assembly will also enable the physician tolater replicate the same positions for subsequent therapeutic and/ordiagnostic procedures, e.g., to enable the physician to administer aprescribed treatment regimen over time and/or to later monitor theeffects of earlier therapeutic procedures.

By using computer-assisted reconstruction algorithms, current ultrasonicimaging systems enable physicians to view a representation of thepatient's interior intravascular structures in both two and threedimensions (i.e., so-called three dimensional or longitudinal viewreconstruction). To this end, image reconstruction algorithms employdata-averaging techniques which assume the intravascular structurebetween an adjacent pair of data samples is an average of each such datasample, i.e., the algorithms use graphical “fill in” techniques todepict a selected section of a patient's vascular system underinvestigation. Of course, if data samples are not sufficiently closelyspaced, lesions and/or other vessel abnormalities may go undetected,since they might lie between a pair of data samples and thereby be“masked” by the image reconstruction algorithms.

As such, current reconstruction algorithms depend upon the ability toobtain and process very precisely longitudinally separated data samplesof a section of a patient's vascular system under investigation. To thisend, automated longitudinal translation of a distally located ultrasoundimaging element is often employed to ensure the data samples areprecisely spaced. For example, U.S. Pat. No. 5,485,486 discloses animaging system in which an ultrasound imaging transducer is mounted on adistal tip of a rotating cable extending through a lumen of a catheterplaced in a patient's vascular system, wherein the distal tip of therotating cable is translated longitudinally at a precise constant ratethrough the use of a longitudinal translation assembly. In particular,the longitudinal translation assembly enables a series of preciselyseparated data samples to be obtained thereby minimizing (if noteliminating) distorted and/or inaccurate reconstructions of theultrasonically scanned vessel section, i.e., since a greater number ofmore closely spaced data samples can reliably be obtained. Further, aprecisely controlled pullback speed makes it possible to takemeasurements in a longitudinal direction, e.g., a lesion length.

Notably, a main advantage of this automated pullback assembly is that itcan be operated in a “hands-off” manner which allows the physician todevote his or her attention entirely to the real-time images with theassurance that all sections of the vessel are displayed. On the otherhand, the disclosed system is relatively large and can be cumbersome fora physician to set up, in part because the longitudinal translationassembly and a rotary drive motor used to rotate the imaging cable musteach be wrapped in separate sterile drapes (i.e., plastic bags) in orderto perform the imaging procedure.

U.S. Pat. No. 5,361,768 discloses an improved system over that disclosedin U.S. Pat. No. 5,485,486, in that a single drive unit provides therequisite longitudinal and rotational translation of the imaging cable.However, the respective rotational and longitudinal movement of thecable is still provided by separate motors, thereby making the“combined” drive unit larger and heavier than either of the previousseparate units.

Thus, it remains desirable to provide a still further improved driveunit for both rotational and precisely controlled translational movementof an imaging cable in an ultrasonic catheter imaging system.

SUMMARY OF THE INVENTION

The present invention is directed to an ultrasonic imaging systememploying a single motor drive unit for providing both rotational andcontrolled longitudinal translation of an operative imaging cabledisposed in a catheter assembly, thereby reducing the size, weight andcost of the system drive unit(s), while at the same time making theimaging system easier to set up and operate.

In a preferred embodiment, the imaging system includes an imagingcatheter assembly secured to a single motor drive unit, wherein theimaging catheter assembly generally comprises an outer guide sheathhaving an operative drive-cable and mounted transducer disposed therein.The motor drive unit includes a main body casing that houses a motorthat rotates a drive-shaft at a specific and predetermined rotationaldrive-shaft speed.

The main body casing includes one or more guide rails that are slidinglymounted on a pullback carriage, such that the main body casing may movelongitudinally relative to the pullback carriage. A rigid “pullback arm”is connected at one end to the pullback carriage and at the other end tothe proximal opening of the outer guide sheath of the catheter assembly,i.e., such that the main body casing is also movable relative to theouter guide sheath of the catheter assembly as the pullback carriageslides along the guide rail(s). A telescoping inner catheter sheathextends through the fixed proximal opening of the outer guide sheath andis attached to the main body casing of the motor drive unit, with thedrive-cable extending through the inner sheath and attached to the motordrive-shaft within the hub, i.e., such that rotation of the motordrive-shaft correspondingly rotates the drive-cable.

In accordance with a first aspect of the invention, the imaging systemcan be made to operate in an automated longitudinal translation mode,wherein the main body casing of the drive unit is made to uniformly andlongitudinally move relative to the pullback carriage by the drive unitmotor, thus causing coincident longitudinal movement of the drive-cable(and distally located transducer) relative to the outer guide sheath ofthe catheter assembly.

In particular, a reduction gear mechanism is mounted circumferentiallyaround the drive-shaft within the main body casing of the drive unit,with the reduction gear mechanism producing an output circumferentialspeed that is significantly less than the circumferential speed of thedrive-shaft. A longitudinal drive train, such as, e.g., a drive screwand threaded collar, is rotatably mounted to the main body casing of thedrive unit, engaging the reduction gear mechanism. In order to providelongitudinal movement of the main body casing relative to the pullbackcarriage, (i.e., while the later is in a fixed, or mounted position), anengagement mechanism associated with the pullback carriage and urged byan expansion spring is caused to engage the threads of the drive screw.Notably, because the circumferential speed of the drive screw is muchless than, but linearly proportional to the circumferential speed of thedrive-shaft, the main body casing moves relative to the pullbackcarriage at a rate that is linearly proportional to the motordrive-shaft speed.

In accordance with a further aspect of the invention, a mechanicaldisengagement member may be provided integral with a distal portion ofthe main body casing of the motor drive unit, which acts as a limitswitch to prevent further longitudinal movement of the main body casingrelative to the pullback carriage. In particular, the mechanicaldisengagement member is preferably provided in a position relative tothe engagement mechanism such that as the main body casing reaches itsmost “proximal” position relative to the pullback carriage (i.e.,farthest from the distal end of the main guide sheath of the catheterassembly, the mechanical disengagement member makes contact with theengagement mechanism, thereby disengaging the engagement mechanism fromthe drive screw to prevent further longitudinal translation of the mainbody casing relative to the pullback carriage.

In accordance with a still further aspect of the invention, adepressible start indicator button may be provided on the main bodycasing such that the body of the pullback carriage mechanicallydepresses the start indicator when the main body casing of the driveunit is at its most “distal” position relative to the pullback carriage.As the main body casing automatically and longitudinally movesproximally relative to the pullback carriage, the pullback carriagemoves away from (i.e., “releases”) the start indicator button, causing asignal to be transmitted to a controller that the automated longitudinaltranslation mode has commenced.

In accordance with a still further aspect of the invention, a selectivelatch may be provided that is operatively associated with the engagementmechanism, and which allows the motor drive unit to be selectivelyoperated in or out of the automated longitudinal translation mode. Byway of example, in a preferred embodiment, the latch comprises anengagement tab and a ball detent mechanism. In particular, when theengagement tab is moved away from the main body casing, the engagementmechanism and the drive screw are engaged, with the expansion springmaintaining the drive unit in an automated longitudinal translationmode. Conversely, when the engagement tab is moved toward the main bodycasing of the drive unit, the engagement mechanism and the drive screware disengaged, with the ball detent mechanism maintaining the driveunit out of an automated longitudinal translation mode.

In accordance with a still further aspect of the invention, a disposablebase plate may be removably mounted to the pullback carriage, allowingfor the motor drive unit to be stably placed on a support structure suchas a table. In a preferred embodiment, the cross-section of the baseplate is preferably U-shaped for easy adaptation to the patient's leg.

Other and further objects, features, aspects, and advantages of thepresent invention will become better understood with the followingdetailed description of the preferred embodiments illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The drawings illustrate both the design and utility of preferredembodiments of the present invention, in which:

FIG. 1 is a schematic view of a vascular ultrasonic imaging systemaccording to the present invention;

FIG. 2 is a cut-away, partial side view of a drive unit employed withthe vascular ultrasonic imaging system of FIG. 1;

FIG. 3 is a cross-sectional view taken along lines 3—3 in FIG. 2;

FIG. 4-A is a plan view of an engagement mechanism and ball detentmechanism employed in the vascular ultrasonic imaging system of FIG. 1;

FIG. 4-B is a side view of the engagement mechanism and ball detentmechanism of FIG. 4-A, shown in an engaged position;

FIG. 4-C is a side view of the engagement mechanism and the ball detentmechanism of FIG. 4-A, shown in a disengaged position;

FIG. 5 is a partial side view of the vascular ultrasonic imaging systemof FIG. 1, prior to initiation of an a utomated ultrasonic imaging scan;

FIG. 6 is a partial side view of the vascular ultrasonic imaging systemof FIG. 1, during an automated ultrasonic imaging scan;

FIG. 7 is a partial side view of the vascular ultrasonic imaging systemof FIG. 1, after termination of an automated ultrasonic imaging scan;and

FIG. 8 is a partial side view of the vascular ultrasonic imaging systemof FIG. 1, illustrating an alternate method of performing an automatedultrasonic imaging scan.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, an exemplary ultrasonic imaging system 20 generallycomprises a flexible imaging catheter assembly 24 connected to a singlemotor drive unit 22, with the motor drive unit 22 in electricalcommunication with an imaging reconstruction console 26 via a power/datacommunications cable 25. The image reconstruction console 26 generallycomprises a controller, data interpretation unit, monitor, keyboard,etc. (not individually shown), wherein the power/data cable 25 transmitsinput/output data to and from the motor drive unit 22, and also providesDC electrical power.

In accordance with constructions well-known in the art, the catheterassembly 24 generally includes a hollow, outer sheath 28, which definesa longitudinal axis 30 along its axial center. A rotatable drive-cable34 extends through the outer sheath 28 and has an ultrasonic transducer36 mounted at its distal end. In a manner described in greater detailbelow, a reduced diameter, telescoping inner catheter sheath 38 extendsfrom a relatively proximal position (designated by arrow 37) within theouter sheath 28, through a proximal end 40 of the outer sheath 28, andis attached to the motor drive unit 22. The drive-cable 34 extendsthrough the inner sheath 38 and is engaged to a motor drive-shaft 64(shown in FIG. 2) within the motor drive unit 22.

Notably, the overall length of the catheter assembly 24 is selected forthe desired diagnostic and/or therapeutic intravascular procedure. Forexample, the overall length of the catheter assembly 24 may berelatively shorter for direct (e.g., arteriotomy) insertions as comparedto the length needed for percutaneous distal insertions (e.g., via thefemoral artery). For ease in illustration, however, only the veryproximal (i.e., adjacent the motor drive unit 22) and distal (i.e., atthe far tip) portions of the catheter assembly are shown in FIG. 1. Byway of non-limiting examples, exemplary preferred imaging catheterassembly constructions in accordance with the general descriptionprovided herein may be found in U.S. Pat. Nos. 5,000,185, 5,115,814,5,464,016, 5,421,338, 5,314,408 and 4,951,677, each of which is fullyincorporated herein by reference.

The motor drive unit 22 broadly includes a main body casing 42, apullback carriage 48, and a rigid pullback arm 54. The main body casing42 houses the electromechanical elements that cause the drive-shaft 34to rotate about the longitudinal axis 30, as indicated by arrows 43 and46. As disclosed and described below, the main body casing 42 isslidingly mounted to the pullback carriage 48, such that the main bodycasing 42 can be reciprocally and longitudinally moved relative to thepullback carriage 48, as indicated by arrow 50. The pullback arm 54fixes the proximal end 40 of the outer sheath 28 relative to thepullback carriage 48, with the inner sheath 38 and drive-shaft 34extending therethrough and fixedly attached to the main body casing 42.In this manner, as the main body casing 42 reciprocally andlongitudinally moves relative to the pullback carriage 48, therespective telescoping inner sheath 38 and drive-cable 34correspondingly move longitudinally relative to the outer sheath 28.

As will be appreciated by those skilled in the art in view of thedisclosure herein, the telescoping inner sheath 38 must be of asufficient length to accommodate the entire “pullback range” of movementof the main body casing 42 relative to the pullback carriage 48, withoutemerging from the proximal end 40 of the outer sheath 28.

The motor drive unit 22 is also provided with an (optional) base plate118 that is removably mounted to the pullback carriage 48, e.g., by aplurality of protrusions 115 in the pullback carriage 48 that mate withcorresponding openings (not shown) in the base plate 118. Preferably, abottom surface 117 of the base plate 118 is suitably configured suchthat the motor drive unit 22 will be stably supported on a flatstructure (e.g., such as an operating table), while the imaging system20 is in operation. Preferably, the cross-section of the base plate 118(shown in FIG. 3) is “U-shaped” to permit the motor drive unit 22 to besupported on a patient's leg. Notably, the motor drive unit 22 willpreferably be compact and light enough to allow a physician to hold themotor drive unit 22 in his or her hand while performing an imagingprocedure and the base plate 118 need not necessarily be mounted to thepullback carriage 48.

In presently anticipated preferred embodiments, the pullback arm 54 andbase plate 118 will be disposable and supplied in sterile packagingseparate from the main body casing 42. Thus, to ensure sterility of allof the components, a relatively thin sterile plastic bag 31 is placedover the main body casing 42 and pullback carriage 48 prior to use. Anopening 32 formed at one end of the sterile bag 31 to allow for thecatheter assembly 24 to be connected therethrough to the main bodycasing 42. The sterile bag 31 is also provided with a tubular portion 23at an opposite end of the main body casing 42 to maintain sterility ofthe power/data cable 25. The back end portion 23 of the sterile bag 31preferably extends at least three feet along the power/data cable 25 toprevent the cable 25 from violating the sterile field. Notably, the baseplate 118 can preferably be snapped onto the base of the pullbackcarriage 48 through the relatively thin sterile bag 31, withoutviolating the sterile field.

As will be apparent to those skilled in the art, an advantage of thepresent invention is that, unlike the prior art in which separatesterile drapes need to be used for each of the rotary drive unit and thelongitudinal drive unit, only a single sterile drape needs to be used inconjunction with operation of the motor drive unit 22.

Referring to FIG. 2, a drive motor 62, such as a DC brushless motor, isfixably supported within the proximal end of the main body casing 42 ofthe motor drive unit 22 by a motor support bracket 66. The motor supportbracket 66 is attached at the proximal end of the main body casing 42 bysuitable means, e.g., such as screws or bonding material (not shown).The drive-cable 34 is mechanically and rotationally coupled to the drivemotor 62 through a rigid drive-shaft 64 that extends through the mainbody casing 42. The drive-shaft 64 is connected at its proximal end tothe drive motor 62, and at its distal end 44 to a motor drive-catheterinterface 67, which is itself connected to the proximal end of thedrive-cable 34.

More particularly, the proximal end 40 of the outer guide sheath 28 isbonded to a cylindrically concave clamping collar 86 having an axialaperture through which the telescoping inner sheath 38 extends. A distalend of the rigid pullback arm 54 is adapted to attach to the clampingcollar 86 to provide a secure, non-slip connection between the pullbackarm 54 and the outer guide sheath 28, without collapsing the outer guidesheath 28. The proximal end of the pullback arm 54 is adapted to beremovably attached to the pullback carriage 48 by a snap (or “clip”)connection 68. In this manner, the outer guide sheath 28 may be securedto the pullback carriage 48, such that the main body casing 42 and,thus, the respective inner telescoping sheath 38 and drive-cable 34 arelongitudinally movable relative to the proximal end 40 of the outerguide sheath 28.

In a manner well-known in the art, the proximal portion of the innersheath 38 is formed into an expanded cylindrical shape, including aconcave clamping collar 69 that is adapted for attachment to the mainbody casing 42 of the motor drive unit 22. A fluid flush port 73 isprovided to access the lumen 75 formed by the inner sheath 38, whereinthe fluid thereby accesses the entire inner lumen area of the catheterassembly 24, i.e., throughout the lumen 53 formed by the outer guidesheath 28 and surrounding the transducer 36 at the distal end thereof.In order to prevent leakage, which can be problematic due to therelative high fluid pressures employed during an imaging procedure, afirst fluid seal 52 is placed at the bond connection between the outerguide sheath 28 and pullback arm clamping collar 86, and a second fluidseal 85 is placed around the proximal end of the drive-cable 34, i.e.,adjacent the motor drive-catheter interface 67.

As will be appreciated by those skilled in the art, the motordrive-catheter interface 67 is axially disposed within a stationaryring-bearing 65 and makes both electrical and mechanical connectionswith the drive-shaft 64. In a presently preferred embodiment, theelectrical connection comprises a coaxial connection between a firstcoaxial cable (not shown) extending through the drive-cable 34 (i.e.,from the transducer 36 to the motor drive-catheter interface 67) and asecond coaxial cable (also not shown) in the drive-shaft 64. Within themotor drive unit 22, a rotary coupler 74 is disposed about the distalend of the drive-shaft 64 and fixably mounted to the main body casing42. In particular, the rotary coupler 74 includes a rotator element (notshown) disposed in the drive-shaft 64 and electrically coupled to thecoaxial cable, in inductive communication with a stationary statorelement (also not shown), wherein the stator element is electricallycoupled to signal generation and processing circuitry (not shown).

As will be appreciated by those skilled in the art, the rotary coupler74 may alternately be located within the proximal portion of thecatheter assembly body 24, (i.e., such that the motor drive-catheterinterface 67 is merely a mechanical interface, and not an electricalinterface), which is a technique currently employed in most commerciallyavailable imaging catheter systems.

An optical encoder 70 is also disposed around the drive-shaft 64 andfixably mounted to the main body casing 42, and provides rotationalspeed feedback data to the console controller 26 to control the drivemotor 62. Alternately, a DC voltage from a servo affixed to the motorcould be used to control the motor speed. Alternately, the drive motor62 may be a stepper motor, so that the console controller 26 can operatethe motor 62 via the power/data cable 25 at an exact and predeterminedrotational speed, without requiring the optical encoder 70.

Referring to FIG. 3 in addition to FIG. 2, the pullback carriage 48 hasa yoke-shaped portion 76 that forms a pair of opposing collars 78, eachof which slidingly engages a respective slide rail 80 extending throughthe main body casing 42. In particular, the respective slide rails 80are each rigidly fixed at one end to the motor support bracket 66 and atthe other end to a support flange 84, which itself is mounted to adistal end of the main body casing 42. In this manner, the main bodycasing 42 is “slidably mounted” to the pullback carriage 48.

In accordance with a more particular aspect of the invention, the drivemotor 62 is operatively coupled to the pull back carriage 48 through areduction gear mechanism 88 and drive screw 90, respectively. Inparticular, the reduction gear mechanism 88 is disposed about thedrive-shaft 64 and fixably mounted to the main body casing 42 so that,as the drive-shaft 64 rotates, a coupling gear 92 of the reduction gearmechanism 88 rotates in the same axial orientation with acircumferential speed that is significantly less than thecircumferential speed of the rotating drive-shaft 64.

The drive screw 90 is rotatably mounted at one end to the motor supportflange 66, and at the other to the distal end support flange 84, asindicated by the respective arrows 82 and 83. The drive screw 90 has acircumferentially disposed drive gear 94 that is engaged with thecoupling gear 92 of the reduction gear mechanism 88 such that, uponrotation of the drive-shaft 64, the drive screw 90 rotates in the sameaxial orientation at a circumferential speed that is much less than, butlinearly proportional to, the circumferential speed of the drive-shaft64. Notably, any number of gear sizes and ratios may be employed betweenthe coupling gear and the drive gear, depending on design choice.

Referring additionally to FIGS. 4A-C, the pullback carriage 48 includesa widthwise axial opening 99 housing a cylindrical pin 101 about whichan engagement mechanism 97 having a threaded end 96 (e.g., a threadedcollar or the like) is rotatably mounted, i.e., such that the engagementmechanism 97 may pivot about the pin 101. An expansion spring 98contained within the pullback carriage 48 is positioned in a manner thaturges the threaded end 96 of the engagement mechanism 97 to engage thethreads of the drive screw 90. When so-engaged, rotation of the drivescrew 90 about its longitudinal axis will translate into a controlledand uniform longitudinal displacement of the main body casing 42relative to the pullback carriage 48, (i.e., during operation of thedrive motor 62), thereby resulting in a coincidental translation of thedrive-cable 34 relative to the outer guide sheath 28.

Engagement of the threaded end 96 of the engagement mechanism 97 withthe threads of the drive screw 90 is controlled by a latch mechanism 56,which allows the imaging system 20 to be selectively operated in an“automated longitudinal translation mode.” The latch mechanism 56includes an engagement tab 57 and a ball detent mechanism 59, whichalternately provide for engagement and disengagement of the engagementmechanism 97 and drive screw 90.

The engagement tab 57 is attached to, and preferably integral with, theengagement mechanism 97, wherein movement of the engagement tab 57toward or away from the main body casing 42 will cause the engagementmechanism 97 to reciprocally rotate about the pin 101, with its threadedend 96 alternately engaging and disengaging the drive screw 90. The balldetent mechanism 59 is attached to, and preferably integral with, thepullback carriage 48, and includes a ball 103 that is partially urgedout of an opening 107 by a spring 105. The ball detent mechanism 59 ispositioned such that the ball 103 will alternately engage a recess 109formed in a distal end of the engagement mechanism 97 when theengagement tab 57 is moved toward the main body casing 42 (i.e., fromthe position shown in FIG. 4-B to the position shown in FIG. 4-C).

In particular, the engagement between the ball 103 and the recess 109creates a countervailing torque to that created by the expansion spring98 on the engagement mechanism 97 about pin 101. In this manner, thethreaded end 96 of the engagement mechanism 97 and the drive screw 90are maintained in a disengaged position, absent the continuedapplication of external force on the engagement tab 57. Contrariwise, asthe engagement tab 57 is moved away from the main body casing 42 (i.e.,from the position shown in FIG. 4-C to the position shown in FIG. 4-B),the recess 109 is forced to disengage the ball 103, and thus theengagement mechanism 97 and the drive screw 90 become engaged. Theexpansion spring 98 exerts enough force on the engagement mechanism 97to maintain an engaged position with the drive screw 90, absent thecontinued application of external force on the engagement tab 57.

As will be appreciated by those skilled in the art, the respectivethreads of the drive screw 90 and engagement mechanism 97, as well asthe rotation orientation of the drive screw 90, are selected so as toeffect relative longitudinal shifting of the pullback carriage 48 fromthe distal end of the drive screw 90 toward the proximal end thereof,i.e., relative to the catheter assembly 24). However, these parameterscould be changed so as to effect a reverse (i.e., proximal to distal)relative displacement of the pullback carriage 48, if desired.

Preferably, the reduction ratio of the reduction gear mechanism 88 isrelatively high, e.g., 100:1, so that the circumferential speed of thedrive screw 90 rotating about its longitudinal axis is much slower thanthat of the drive-shaft 64, thereby resulting in a slow and controlledlongitudinal movement of the drive-cable 34 (e.g., about 1 mm/second).Of course, other longitudinal translation rates may be provided byvarying the output parameters of the drive motor 62, reduction gearmechanism 88, drive screw 90, coupling gear 92, and/or drive gear 94.

Notably, using a reduction gear mechanism 88 with such a high reductiongear ratio allows for a minimal amount of power is used to rotate thedrive screw 90 about its longitudinal axis. As a result, the size of thedrive motor 62 can be minimized and need not be any larger than thattypically used to rotate a drive-cable. Further, in alternate preferredembodiments, the reduction gear mechanism 88 may be provided withmultiple switchable reduction ratios to allow the imaging system 20 toalternately operate with varying longitudinal translation speeds duringan automated longitudinal translation mode.

The imaging procedure (either in or out of the automated longitudinaltranslation mode) can be conveniently commenced or terminated throughthe use of a thumb/finger start switch 108 mounted in an opening 106 ofthe distal end of the main body casing 42, and electrically coupled toselectively actuate the drive motor 62. An LED 110, which indicates thecommencement of an imaging procedure, is also mounted in the opening106, wherein the start switch 108 and LED 110 are positioned such thatthey each pass only a short distance through the opening 106.Alternately, it may be desirable to prevent inadvertent movement of theswitch 108, (e.g., to prevent inadvertent actuation of the motor drive62), in which case the switch 108 should be sized and located such thatit is accessible without extending through the opening 106.

A proximally extending mechanical disengage member 112, which ispreferably integral with the support flange 84, acts as a limit switchto prevent the drive gear 94 of the drive screw 90 from making contactwith the distal face of the pullback carriage 48 during the automatedlongitudinal translation mode. In particular, as the distal face of thepullback carriage 48 “approaches” the drive gear 94, the mechanicaldisengage member 112 “approaches” the engagement mechanism 97. Thelength of the disengage member 112 is preferably selected such that,immediately prior to the drive gear 94 making contact with the distalface of the pullback carriage 48, the proximal end of the mechanicaldisengage member 112 makes contact with, thereby rotating the engagementmechanism 97 about pin 101 in a manner that disengages the threaded end96 of the engagement mechanism 97 from the drive screw 90. This movementwill also cause the ball 103 to engage the recess 109, thereby lockingthe engagement mechanism 97 away from the drive screw 90.

An electric start indicator 114 is mounted to the drive motor supportflange 66, and is electrically coupled to the console controller 26 viathe power/data cable 25 to indicate the commencement of the automatedlongitudinal translation mode. In particular, prior to commencement ofthe automated longitudinal translation mode, an actuating button 116mounted on the start indicator 114 is depressed by the proximal face ofthe pullback carriage 48, as the later is placed in a starting positionrelative to the main body casing 42. When the automated longitudinaltranslation mode is commenced, the pullback carriage 48 moves away from,thereby releasing the button 116 and causing a corresponding signal tobe sent from the start indicator 114 to the console controller 26.

As will be appreciated from the present disclosure by those skilled inthe art, if desired, a similar mechanically actuated switch could beprovided at the distal end of the main body casing (i.e., attached tothe front support bracket 84) to indicate that a pullback procedure iscomplete.

As depicted on FIG. 5, the motor drive unit 22 preferably includes ascale 120 mounted on the outside of the main body casing 42. A pointer122 attached to, and preferably integral with, the pullback carriage 48is positionally associated with the scale 120 to provide informationregarding the longitudinal movement of the transducer 36 betweenrespective starting and ending positions within the outer guide sheathduring a pullback procedure, i.e., longitudinal movement of the mainbody casing 42 relative to the pullback carriage 48 over an incrementaldistance will effect a corresponding movement of the transducer 36relative to its most distal position within the outer guide sheath 28 bythat same incremental distance.

With reference to FIGS. 5-8, operation and use of the imaging system 20is now described. The motor drive unit 22 is initially manually placedin its “starting” position, i.e., the main body casing 42 is placed atits most distal position relative to the pullback carriage 48—so thatthe proximal face of the pullback carriage 48 depresses the actuatorbutton 116 on the start indicator 114. The physician or other hospitalpersonnel can perform this step by sliding the engagement tab 56 towardthe main body casing 42, so that the engagement mechanism 97 isdisengaged from the drive screw 90. The pullback carriage 48 can then bemoved proximally while grasping the main body casing 42. To preventinadvertent movement from the starting position, the motor drive unit 22should be locked into position by sliding the engagement tab 56 awayfrom the main body casing 42 such that the threaded end 96 of theengagement mechanism 97 engages the drive screw 90.

The catheter assembly is attached to the motor drive unit 22, i.e., withthe clamping collar 69 attached to the main body casing 42 through thesterile bag 31 and the motor drive-catheter interface 67 connected tothe drive-shaft 64. If longitudinal translation of the transducer 36 isdesired during the image scanning procedure, the pullback arm 54 isattached at one end to the pullback carriage 48 and at the other to theclamping collar 86 attached to the outer guide sheath 28.

The attending physician can then insert the outer guide sheath 28through a hemostasis valve 136 in the patient's body and position theouter guide sheath 28 and the transducer 36 within the vessel of thepatient to be examined using standard fluoroscopic techniques and/or thetechniques, such as those disclosed and described in U.S. Pat. No.5,115,814, which is incorporated herein by reference. As is well-knownin the art, the distal end of the outer guide sheath 28 should bepositioned such that the entire portion of the vessel of interest can beeffectively image scanned without requiring its relocation.

With the catheter 24 and the motor drive unit 22 in place, the physicianmay conduct an imaging scan of the patient's vessel by operating thestart switch 108 to cause the high-speed rotation of the drive-shaft 64and, correspondingly, the drive-cable 34 and transducer 36. Notably, ifthe physician desires only to provide a data sample associated with asingle transverse section of a patient's vessel, prior to operating thestart switch 106, he or she should slide the engagement tab 56 towardthe main body casing 42 to disengage the engagement mechanism 97 fromthe drive screw 90.

Alternatively, the physician may elect to perform an automatedultrasonic imaging scan by operating the imaging system 20 in theautomated longitudinal translation mode. In such a situation, thetransducer 36 will be shifted longitudinally at a constant ratesimultaneously with the high-speed rotation of the transducer 36. Datasamples representing longitudinally spaced-apart 360° “slices” of thepatient's interior vessel walls can thereby be accumulated, which can bereconstructed using known algorithms and displayed in two- orthree-dimensional formats on the console monitor (part of 26, notshown).

Prior to any longitudinal translation of the transducer 36 relative tothe outer guide sheath 28, the transducer 36 is preferably positioned atthe most distal portion of the vessel to be scanned, since the imagingsystem 20 will produce a “distal-to-proximal” scan of the patient'svessel. Once the outer guide sheath 28 and the transducer 36 have beenpositioned in a region of the patent's vessel in which the physiciandesires to observe, the motor drive unit 22 is positioned to remove anyunnecessary slack in the guide sheath 28.

In order to facilitate the automated longitudinal translation process,the base plate 118 may be attached to the pullback carriage 48 (i.e.,through the sterile plastic bag 31) in order to support the motor driveunit 22, e.g., on a support structure such as a table, or on thepatient's leg. As noted briefly above, the transducer 36 is mostpreferably translated in a distal-to-proximal direction by means of themotor drive unit 22 (i.e., in the direction of arrow 126 in FIGS. 5 and6).

In FIG. 5, the motor drive unit 22 is shown in a position at thebeginning of an automated ultrasonic imaging scan, it being noted thatthe pointer 122 on the pullback carriage 48 registers with the “0”marking on the scale 120. Prior to operating the starting switch 108,the physician must slide the engagement tab 56 away from the main bodycasing 42 to engage the engagement mechanism 97 to the drive screw 90.The physician will then initiate the automated ultrasonic imaging scanby operating the start switch 108, which causes the main body casing 42to longitudinally and proximally move relative to the pullback carriage48 (i.e., in the direction of arrow 128 in FIGS. 5 and 6). As theproximal face of the pullback carriage 48 moves away from startindicator 114, the actuator button 116 is released, thereby causing asignal to be sent to the console controller 26 indicating that theautomated ultrasonic imaging scan has been initiated. Alternately, thephysician could start the motor switch 108 first, and then, by slidingthe engagement tab 56 away from the main body casing 42, the pullbackprocess is started.

With the motor drive unit 22 supported on the base plate 118, thepullback carriage 48 and, thus, the pullback arm 54 will remain “fixed,”regardless of the longitudinal movement of the main body casing 42. Assuch, the outer guide sheath 28 will remain fixed by the pullback arm54. A proximal longitudinal movement of the main body casing 42 willresult in a corresponding proximal longitudinal movement of therespective drive-cable 34 and telescoping inner sheath 38 relative tothe outer guide sheath 28. Consequently, the transducer 36 willproximally and longitudinally move from its most distal position(indicated by a vertical axis line 124) a distance equal to that movedby the main body casing 42 relative to the pullback carriage 48, asregistered by the pointer 122 on the scale 120.

In FIG. 7, the motor drive unit 22 is shown in a position at the end ofan automated ultrasonic imaging scan, it being noted that the pointer122 on the pullback carriage 48 now registers with the “10” marking onthe scale 120.

Rather than supporting the motor drive unit 22 on the base plate 118,the physician may instead elect to hold the main body casing 42 of themotor drive unit 22 in his or her hand. In this instance, while keepingthe portion of the outer guide sheath 28 between the clamping collar 86and the hemostasis valve 136 sufficiently straight, the physician mayinitiate the automated ultrasonic imaging scan with the same effect asdescribed above by manually moving the main body casing 42longitudinally and proximally at approximately the same rate as thatwhich the pullback carriage 48 travels relative to the main body casing42. This “matching of speeds” can be facilitated by maintaining auniform tension in the outer guide sheath 28 between the clamping collar86 and hemostasis valve 136, while moving the main body casing 42.

Referring to FIG. 8, the physician can alternately prevent the main bodycasing 42 of the motor drive unit 22 from moving proximally during theautomated ultrasonic imaging scan. In particular, with the main bodycasing 42 in a fixed position, the pullback carriage 48 and, thus, thepullback arm 54, longitudinally and distally move in the direction ofarrow 130. As a result, the distance between the clamping collar 86 andthe hemostasis valve 136 decreases. Since the outer guide sheath 28 isanchored by the clamping collar 86 and the hemostasis valve 136, theouter guide sheath 28 is laterally deflected or “bowed.” Such lateraldeflection of the outer guide sheath 28 causes the telescoping innersheath 38 and, thus, the drive-cable 34, to longitudinally move in thedirection of arrow 132, i.e., from its most distal position a distanceequal to that moved by the main body casing 42 relative to the pullbackcarriage 48, as registered by the pointer 122 on the scale 120.

In this later situation, as the main body casing 42 reaches its mostproximal position relative to the pullback carriage 48, the mechanicaldisengage member 112 contacts and disengages the engagement mechanism 97from the drive screw 90, terminating the automated ultrasonic imagingprocess. Upon the main body casing 42 reaching its most proximalposition relative to the pullback carriage, the pointer 122 on thepullback carriage registers with the marking “10” on the scale 120. Ofcourse, the automated ultrasonic imaging procedure need not necessarilybe conducted over the entire range of “0-10” marked on the scale 120(i.e., the fullest possible range of movement of the main body casing 42relative to the pullback carriage 48), but instead could be terminatedat any time, i.e., by sliding the engagement tab 56 toward the main bodycasing 42 to disengage the engagement mechanism 97 from the drive screw90.

In certain instances, a physician may wish to provide data samplesassociated with discrete and different transverse sections of thepatient's vessel, without necessarily accumulating the data frommultiple, equally spaced slices. For instance, it may be desirable toanalyze discrete images of selected areas of the patient's vessel. Insuch a case, the physician can operate the imaging system 20 in a manuallongitudinal translation mode by sliding the engagement tab 56 towardthe main body casing 42 to disengage the engagement mechanism 97 fromand the drive screw 90. The physician can then manually move the mainbody casing 42 relative to the pullback carriage 48 to place therotating transducer 36 in the desired portion of the patient's vessel tobe imaged. The exact relative position of the transducer 36 can bedetermined by referring to the position indicated by the pointer 122 onthe scale 120.

Those skilled in this art will recognize that a number of alternativemechanical and/or electrical means could be employed in theafore-described preferred embodiments. For example, rather than thedrive screw 90 and engagement mechanism 97 assembly, a drive gear andrack assembly, or a drive belt assembly may be employed tolongitudinally translate the main body casing 42 relative to thepullback carriage 48. Examples of these alternatives are disclosed anddescribed in co-pending U.S. patent applications Ser. No. 08/722,325,entitled “Device for Controlled Longitudinal Movement of an Operativeelement Within a Catheter Sheath and Method” and U.S. Ser. No.08/721,433, entitled “Catheter System and Drive Assembly Thereof,” whichare each fully incorporated herein by reference.

Also, rather than the engagement tab 57 and ball detent mechanism 59,locking slides, latches or quarter-turn screws could be used to allowengagement and disengagement of the threaded end 96 of the engagementmechanism 97 to and from the drive screw 90.

Still further, as opposed to the power/data cable 25, power could besupplied by batteries and data/instructions could be transmitted usingradio frequency transmitters and receivers so as to make the motor driveunit 22 entirely self-contained.

Further still, various automated longitudinal translation rates may beselected for various purposes. For example, slow rates give ample timefor the physician to examine the real-time images in cases where time isnot a limiting factor. The upper rate limit is governed by thetransducer 36 rotation rate and the effective thickness of the imagingdata slices generated by the probe, such that there is an acceptable gapbetween successive imaging data vectors and slices. This would preventmissing discernible features or vector overwriting during vascularimaging during automated translation of the transducer 36. The effectivethickness is governed by the beam characteristics of the transducer 36.For some applications, the longitudinal translation of the transducer 36may be discontinuous (i.e., gated to an electrocardiogram) for use withmodified algorithms or programmed to translate a fixed distancediscontinuously.

Moreover, while particularly adapted for imaging of vascular regionsusing a transducer 36, the disclosed embodiment of the invention couldbe modified to provide controlled longitudinal movement of otherrotating operative elements such as rotating arthrectomy devices.Furthermore, the invention is not limited for use in vascular regions,but can be also used in other bodily cavities and passages.

Thus, while the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A motor drive assembly, comprising: a main bodyadapted for attachment to a catheter assembly; a motor means housed in,and secured to, the main body; a drive shaft means for rotating anoperative element disposed in the catheter assembly, the drive shaftmeans having a first end rotationally coupled to the motor means and asecond end adapted for rotationally coupling to the operative element; apullback carriage means for slidingly engaging the main body; a drivetrain means rotatably attached to the main body and engagable to thepullback carriage means for causing movement of the pullback carriagemeans relative to the main body when the drive train means is rotated;and a gear means for communicating with the drive shaft means and drivetrain means, such that rotation of the drive shaft means causescorresponding rotation of the drive train means.
 2. The motor driveassembly of claim 1, further comprising a pullback arm means attachableat one end to the pullback carriage means and at the other end to anouter sheath of the catheter assembly, such that, when the drive shaftmeans is coupled to the operative element, movement of the main bodyrelative to the pullback carriage means causes coincidental movement ofthe operative element relative to the outer sheath.
 3. The motor driveassembly of claim 1, further comprising a base plate means attachable tothe pullback carriage means.
 4. The motor drive assembly of claim 1,wherein the main body comprises a pair of guide rail means, and thepullback carriage means comprises a pair of collar means, each collarmeans for slidingly engaging a respective guide rail means.
 5. The motordrive assembly of claim 1, wherein the drive train means comprises: adrive screw means rotatably mounted to the main body for rotationalcommunication with the gear means, and a threaded collar means pivotallymounted to the pullback carriage means and engagable with the drivescrew means for causing translational movement of the main body relativeto the pullback carriage means.
 6. The motor drive assembly of claim 5,wherein the pullback carriage means comprises a latch means foralternately engaging or disengaging the pullback carriage means to orfrom the threaded collar means.
 7. The motor drive assembly of claim 5,further comprising a disengage means attached to the main body fordisengaging the threaded collar means from the drive screw means whenthe main body moves to a predetermined position relative to the pullbackcarriage means.
 8. The motor drive assembly of claim 1, wherein the gearmeans comprises a reduction gear means, such that rotation of the driveshaft means at a first angular velocity causes corresponding rotation ofthe drive train means at a second angular velocity, the second angularvelocity being substantially less than the first angular velocity. 9.The motor drive assembly of claim 1, further comprising a motionindicator means attached to the main body for sending a signal to anexternal controller when the main body moves away from a start positionrelative to the pullback carriage means.
 10. An imaging system,comprising: a) a catheter assembly comprising an outer sheath and anoperative element disposed therein; b) a motor drive assembly meansincluding: i) a main body adapted for attachment to the catheterassembly; ii) a motor means housed in and secured to the main body; iii)a drive shaft means for rotationally coupling the motor means to theoperative element; iv) a pullback carriage means for slidingly engagingthe main body; v) a drive train means rotatably attached to the mainbody and engagable to the pullback carriage means for causing movementof the pullback carriage means relative to the main body when the drivetrain means is rotated; and vi) a gear means for communicatingrotationally with the respective drive shaft means and drive trainmeans, such that rotation of the drive shaft means causes correspondingrotation of the drive train means; and c) a pullback arm means forcausing coincidental movement of the operative element relative to theouter sheath upon movement of the main body relative to the pullbackcarriage means when the drive shaft means is coupled to the operativeelement.
 11. The imaging system of claim 10, further comprising a baseplate means attachable to the pullback carriage means.
 12. The imagingsystem of claim 10, wherein the main body comprises a pair of guide railmeans, and the pullback carriage means comprises a pair of collar means,each collar means for slidingly engaging a respective guide rail means.13. The imaging system of claim 10, wherein the drive train meanscomprises a drive screw means rotatably mounted to the main body forcommunicating rotationally with the gear means, and a threaded collarmeans pivotally mounted to the pullback carriage means and engagablewith the drive screw means for causing translational movement of themain body relative to the pullback carriage means.
 14. The imagingsystem of claim 13, wherein the pullback carriage means comprises alatch means for alternately engaging or disengaging the pullbackcarriage means to or from the threaded collar means.
 15. The imagingsystem of claim 14, further comprising a disengage means attached to themain body for disengaging the threaded collar means from the drive screwmeans when the main body moves to a predetermined position relative tothe pullback carriage means.
 16. The imaging system of claim 10, whereinthe gear means comprises a reduction gear means, such that rotation ofthe drive shaft means at a first angular velocity causes correspondingrotation of the drive train means at a second angular velocity, thesecond angular velocity being substantially less than the first angularvelocity.
 17. A motor drive assembly, comprising: a main body means forattaching to a catheter assembly; a pullback carriage means forslidingly engaging the main body means; a motor means housed in the mainbody means for rotationally coupling to a drive shaft means; a drivetrain means for rotationally coupling the main body means to the driveshaft means, the drive train means being engagable to the pullbackcarriage means for causing movement of the pullback carriage meansrelative to the main body means when the drive shaft means is rotated.18. The motor drive assembly of claim 17, further comprising a gearreduction means for communicating rotationally with the respective driveshaft means and drive train means, such that rotation of the drive shaftmeans causes corresponding rotation of the drive train means at asubstantially slower angular velocity.